This proposal seeks to facilitate radiation therapy for patients with prostate cancer. Recent studies have demonstrated that increasing radiation dose improves the likelihood of disease control of prostate cancer. The current doses under evaluation (70 to 80 Gy) are associated with potentially significant risk of toxicity to the normal organs adjacent to the prostate, especially the rectum. Sparing the rectal wall from potentially toxic doses of radiation, while continuing to treat the peripheral zone of the prostate, involves precise treatment planning and delivery. Ensuring such precise treatment plans do not result in prostate gland underdosage has been only partly handled by pre-treatment localization. Intratreatment physiological movement of the prostate, although demonstrated to be potentially significant (i.e., up to 2 cm), has not yet been addressed clinically. Intratreatment target movement is greatest when patients are positioned prone for treatment, potentially decreasing an observed static advantage of geometric separation of the rectum from the prostate that occurs when patients are placed in the prone position. The hypothesis of this study is that intratreatment prostate movement limits the dose received by the prostate, and that monitoring and reducing this movement will provide increased rectal dose sparing, thus facilitating safe and accurate prostate gland treatment. Descriptive statistics of prostate movement will be acquired using a novel, minimally invasive system for monitoring implanted electromagnetic transponders. The specific aims are to determine the impact of movement on 1) dose to the prostate and 2) dose to the rectal wall. The data from this study will support a subsequent Phase II trial to establish tumor control as well as morbidity reduction in radiotherapy treatments monitored and controlled to minimize intratreatment prostate movement. [unreadable] [unreadable]